diff --git a/pymc/distributions/mixture.py b/pymc/distributions/mixture.py
index 327251b5c35..0e1d82a7153 100644
--- a/pymc/distributions/mixture.py
+++ b/pymc/distributions/mixture.py
@@ -229,7 +229,7 @@ def rv_op(cls, weights, *components, size=None, rngs=None):
         return mix_out
 
     @classmethod
-    def ndim_supp(cls, rng, weights, *components):
+    def ndim_supp(cls, weights, *components):
         # We already checked that all components have the same dimensionality
         return components[0].ndim